Field-induced Conductance Switching by Charge-state Alternation in Organometallic Single-Molecule Junctions

Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These molecular intrinsic properties are usually addressed by varying the molecules electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high to low current ratios exceeding 1000 at voltage stimuli of less than 1.0 V. DFT calculations identify a localized, redox active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarised ground state unique to the Mo centre. This situation opens an additional slow and incoherent hopping channel for transport, triggering a transient charging effect of the entire molecule and a strong hysteresis with unprecedented high low-to-high current ratios.Comment: 9 pages, 4 figure

Electrochemical Multiplexing: Control over Surface Functionalization by Combining a Redox-Sensitive Alkyne Protection Group with "Click"-Chemistry

Local functionalization of surfaces is a current technological challenge. An electrochemically addressable alkyne protection group is presented enabling the site-selective liberation of alkynes exclusively on electrified electrodes. This controlled deprotection is based on a mendione chromophore which becomes a strong enough nucleophile upon reduction to intramolecularly attack the trialkylsilane alkyne protection group. The site-selective liberation of the alkyne is demonstrated by immobilizing the protected alkyne precursor on a transparent TiO2 electrode and subsequently immobilizing red and blue azide dyes by azide-alkyne "click"-chemistry. While the proof-of-principle is based on colorations visible to the bare eye, the technique presented is generic also to nontransparent electrodes, microscale separations, and functional moieties other than dyes. It may open manifold applications where site-selective functionalization is required but hardly realizable with conventional methods

Transport Properties of a Single-Molecule Diode

Charge transport through single diblock dipyrimidinyl diphenyl molecules consisting of a donor and acceptor moiety was measured in the low-bias regime and as a function of bias at different temperatures using the mechanically controllable break-junction technique. Conductance histograms acquired at 10 mV reveal two distinct peaks, separated by a factor of 1.5, representing the two orientations of the single molecule with respect to the applied bias. The current-voltage characteristics exhibit a temperature-independent rectification of up to a factor of 10 in the temperature range between 300 and 50 K with single-molecule currents of 45-70 nA at ±1.5 V. The current-voltage characteristics are discussed using a semiempirical model assuming a variable coupling of the molecular energy levels as well as a nonsymmetric voltage drop across the molecular junction, thus shifting the energy levels accordingly. The excellent agreement of the data with the proposed model suggests that the rectification originates from an asymmetric Coulomb blockade in combination with an electric-field-induced level shifting. © 2012 American Chemical Society.1

Seriously ill hospitalized patients’ perspectives on the benefits and harms of two models of hospital CPR discussions

OBJECTIVE: To describe seriously ill patients’ perspectives on expert-endorsed approaches for hospital cardiopulmonary resuscitation (CPR) discussions. METHODS: We created two videos depicting a hospital doctor discussing CPR with a seriously ill patient. One depicted a values-based approach with a doctor's recommendation, and one an information-focused approach without a recommendation. During semi-structured interviews, 20 seriously ill hospitalized patients viewed and commented on both videos. We conducted a thematic analysis to describe benefits and harms of specific discussion components. RESULTS: Half of participants reported no preference between the videos; 35% preferred the information-focused, and 15% the values-based. Participants’ reactions to the discussion components varied. They identified both benefits and harms with components in both videos,though most felt comfortable with all components (range, 60-65%) except for the doctor's recommendation in the values-based video. Only 40% would feel comfortable receiving a recommendation, while 65% would feel comfortable with the doctor eliciting their CPR preference as in the information-focused video, p=0.03. CONCLUSION: Participants’ reactions to expert-endorsed discussion components varied. Most would feel uncomfortable receiving a doctor's recommendation about CPR. PRACTICE IMPLICATIONS: Participants’ varied reactions suggest the need to tailor CPR discussions to individual patients. Many patients may find doctor's recommendations to be problematic